In certain installations such as a solar heat system in which water is used as the heat transfer medium there is always danger of freeze-up when the flow of water through the heat exchanger is stopped with entrapped water in the heat exchanger. This invention provides a system where the heat exchanger is self-draining when the flow of liquid is interrupted for any reason with the result that there is no danger of this freeze-up. The self-draining feature is, of course, applicable to other heat exchanger systems using a liquid in which it is desirable to drain the liquid containing portion of the system including the heat exchanger automatically when flow of liquid through the system is interrupted either intentionally or accidentally.
One of the features of this invention therefore is to provide a self-draining heat exchanger having a liquid containing part for a heat exchange liquid together with automatic valve means functioning to direct the liquid through its proper path in the system when liquid flow is set up but which opens automatically when liquid flow is interrupted to drain the liquid containing portions of the system using the weight of the liquid to open the valve means.